1. Field of the Invention
The invention relates, in general, to an apparatus and method for stimulating wells, such as oil wells, to improve the production of oil therefrom, and more particularly, to an apparatus and method for increasing the transmissibility of oil from a productive oil bearing formation into which an oil well bore is drilled to increase the flow of oil, or similar fluids, from the formation into the well bore.
2. Description of the Prior Art
Oil wells have been known to produce oil for nearly seventy-five (75) years. Oil wells that have been producing oil for several years often experience a reduction in oil extraction or production as the years progress. When the oil production is reduced, remedial action in the form of stimulation to improve the oil production output of the oil well is undertaken.
Generally, such stimulation may involve improvement of the permeability or transmissibility of the reservoir itself or merely clearing the casing perforations of accumulated production-restricting contaminants, such as heavy hydrocarbons, paraffins, tars, mineral depositions, or formational fines in or near the casing perforations, by the use of vibratory explosive forces created by the ignition of a detonator and detonating cord.
Typically, the methods used to increase the transmissibility of sand, shale or rock formation are shock treatments using explosives, acid washes, hydraulic fracturing, and high energy gas fracturing.
The flow rate of a fluid such as oil through a porous medium, such as a sand, shale or rock formation, is a function of the permeability or transmissibility of that particular formation. If the transmissibility of oil from a oil bearing formational reservoir can be increased, more fluid can be recovered. It is well known that over the life of an oil or gas well, with continued pumping or removal of the oil or gas from that well, the permeability of the surrounding formation may be economically insufficient to justify continued production, even though a large percentage of fluid hydrocarbons remain. When this occurs, the oil well operator can either abandon the oil well or can attempt to increase the permeability of that formation to rejuvenate the flow of liquid hydrocarbons therethrough.
There are currently a number of techniques or processes for mechanically increasing permeability. The best known processes are: (1) hydraulic fracturing; (2) explosive fracturing; (3) acidizing, and (4) high energy gas fracturing.
Hydraulic fracturing is a process used for increasing the permeability of a rock formation by a slow introduction of a highly viscous fluid that is pumped into the area of a well bore between packings. In the hydraulic fracturing technique, the combined fluid pressure is steadily increased until the tensile strength of that particular rock material is exceeded. When this occurs, a fracture will be initiated which propagates from opposite sides of the well bore into the formation; this is known as a biwing fracture. This fracture is induced at a point of least resistance in the rock material.
A fluid used in practicing such a method is one selected to be sufficiently viscous to enable the suspension and mass transport of proppants suspended therein. Such proppant materials are either sand grains or grains of a synthetic material and are made to pass into and settle in the induced fracture. So arranged, the proppants prevent the induced fracture from totally closing once the pressure on the fluid is reduced and the normal closing pressures of the rock formation are re-exerted. Hydraulic fracturing generally involves the generation of the single biwing fracture that extends in a vertical plane from opposite sides of the well bore into the rock formation. In such fracturing, the injected fluids will, by and large, remain in the formation, and the proppants used to support the fracture may, due to compaction, actually come to restrict the permeability of that rock formation rather than enhance or improve its permeability. Another drawback to the use of hydraulic fracturing, and of major consideration in selecting a rock formation fracturing process, is the extent and expense of the equipment and labor involved, since the hydraulic fracturing method requires the use of hydraulic pumps with a high pressure capability along with the temporary positioning of a packer above the oil bearing strata.
In an attempt to overcome the limitations of hydraulic fracturing where generally only a single biwing fracture is produced, explosives have been used for dynamically loading a rock formation. Because of the speed of burning of an explosive, and the shock wave produced thereby, it has been found that explosive compaction of the formation rock around the well bore opposite the explosion may actually decrease rather than increase the permeability of the rock formation. Therefore, while explosive fracturing may provide a greater circumferencial fracturing effect in a rock formation, it may also depredate the permeability of the rock formation to the point where most, if not all, permeability is lost. Explosive fracturing has been, therefore in the past, generally considered unpredictable and unreliable.
Acid fracturing is a process which is utilized to increase permeability by dissolving reactive materials in a rock formation to create conductive passageways or xe2x80x9cworm holesxe2x80x9d and for chemically etching the oppositely disposed faces of a rock formation fracture. The acids which are frequently used are concentrated solutions of hydrofluoric and hydrochloric acid, either of which can, of course, create serious safety problems in the transportation and conveyance of such highly corrosive fluids to a desired location in an oil well bore.
Furthermore, acidizing is limited by a danger of formation matrix collapse due to excessive rock dissolution near the well bore as a consequence of a preferential invasion of the acid used into zones of high, rather than low, permeability.
Another limitation found in the use of the acidizing technique, is that the depth of penetration is limited by the type of rock in the rock formation and the degree of the strength of the acid. Many times, these acidizing processes have been found to cause extensive damage to the well bore due to the geochemical reactions produced. Therefore, the nature of the materials at the location where the fracture is to be induced must be identified prior to selection of the acid to be used. Where such unwanted geochemical reactions take place, they can create damage, leading even to a loss of permeability.
Propellant deflagration is a recent technology that has been developed to produce a good distribution of fractures in the oil-bearing rock formation around a well bore without the problems that have been inherent in the explosive and acid processes.
In the use of high energy gas fracturing, a significant amount of high energy is created by a deflagrated propellant that is ignited in a well bore adjacent to a rock formation to be fractured. Upon ignition of the propellant in the canister, high-energy gas and other products of this combustion process, such as water vapor or steam, are driven to near sonic velocities.
The propellant can be burned radially from a longitudinal center cavity within the propellant, or can be burned from one end, as in a cigarette burn, or a combination of both processes can be employed to develop the high energy fracturing process.
In practice, high-energy gas fracturing involves the placement of a canister of a propellant adjacent to a perforated wall of a well bore in the zone where it is desired to increase the permeability of the oil-bearing rock formation. An igniter rod is then implanted adjacent to the canister containing the propellant. To ignite the propellant, an electrical current is transmitted over one or more electrical wires from the surface above the entrance to the oil well bore to instantaneously detonate an electric blasting cap which initiates deflagration thereof in a period of milliseconds. Once deflagration occurs, a high volume of pressurized gas and water is generated at near sonic velocities. By such deflagration, the energy loading in the oil well bore will be propagated much faster than that which occurs during hydraulic fracturing. Such an increase in the propagation speed of the energy loading produces multiple fractures in directions other than in the plane of least resistance through the oil-bearing rock formation surrounding the oil well bore. The propellant is selected from a group of propellants which will burn at a far slower rate than those propellants used for typical explosive detonations. No destructive shock wave will, therefore, be generated in a propellant deflagration which would cause crumbling of the material around the well bore.
The present invention overcomes the difficulties and problems inherently found in the prior art. To this end, these prior art problems have been overcome by the present invention, providing a new, unique and relatively foolproof, and comparatively inexpensive apparatus and method for rejuvenating and bringing, as it were, xe2x80x9cold maturexe2x80x9d oil wells back into meaningful and cost-effective oil production.
Fundamentally, the basic invention herein is an apparatus and method for increasing the permeability of a productive oil formation about an existing oil well bore to stimulate oil extraction therefrom, comprising a combination of a high pressure detonator igniting a detonating cord with a plurality of hardened steel sleeves thereabout, disposed in a spaced apart relationship at predetermined distances along the detonating cord to effectuate time sequencing of the detonating cord explosions, and the explosive gas propagation/burn rate generated thereby within the oil well bore. An external plastic tube, arranged to be adjacently disposed to the detonating cord and pressure compensators, is filled with special chemicals such as paraffin dispersents, and granulated chemicals containing chlorine, or the like, such that upon ignition of the detonating cord, the granulated chemicals are explosively propelled through the clogged perforations in the oil well casing and into the coagulated geologic formation thereabout to chemically react therewith to promote oil flow therethrough.
Additionally, a protective shield is mounted about the high-pressure detonator for absorbing the shock effect of the detonator when ignition of the detonator occurs in the oil well casing while, at the same time, the kinetic energy force effectuated by the explosion of the detonator is substantially preserved. A Sample/Junk basket and weight are mounted to the bottom of the apparatus to capture formational material for analysis, debris created by the detonation of the detonator and the detonating cord, and drives the entire combination into the typical highly viscous fluid found in oil wells. A 0.092 diameter support wire, to which the detonating cord, detonator, pressure compensators, external plastic tube containing chemicals, Sample/Junk basket and weight are all secured, serves as the back-bone for the apparatus.
There has thus been outlined, rather broadly, the more important features of the invention in order that the detailed description thereof that follows may be better understood, and in order that the present contribution to the art may be better appreciated. There are additional features of the invention that will be described hereinafter and which will form the subject matter of the claims appended hereto.
In this respect, before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting.
As such, those skilled in the art will appreciate that the conception, upon which this disclosure is based, may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention.
Further, the purpose of the foregoing abstract is to enable the United States Patent and Trademark Office, the public generally, and especially the scientists, engineers and practitioners in the art who are not familiar with patent or legal inspection, the nature and essence of the technical disclosure of the application. The abstract is neither intended to define the invention of the application, which is measured by the claims, nor is it intended to be limiting as to the scope of the invention in any way.
It is one object of the present invention herein to provide an apparatus and method for increasing oil production in existing oil wells which embodies many novel features that result in a new apparatus and method for enhancing oil production in existing oil wells which is not anticipated, rendered obvious, suggested, or even implied by any of the prior art cleaning devices, either alone or in any combination thereof.
Another and further object and feature of the instant invention disclosed herein is to provide an apparatus and method for stimulating oil production in a pre-existing oil well utilizing an explosive detonating cord, producing an explosive series of charges which are characterized by a series of sequenced, pressure controlled explosive pulses having predictably known pressure-time characteristics of determinable durations.
An even further object and feature of the instant invention disclosed and described herein is to provide a new apparatus and method for increasing the oil production of an existing oil well, while simultaneously overcoming some of the disadvantages normally associated therewith.
It is a still further primary and important feature and object of the present invention to provide an apparatus and method for stimulating oil well production, utilizing an explosive gas generating charge, which produces a pulsating gas pressure-volume wave.
Another important and primary feature of the present invention is to provide an external plastic tube, arranged in adjacent disposition to the detonating cord and pressure compensators, filled with special chemicals such as paraffin dispersents, such as granulated chemicals containing chlorine, or the like, wherein upon the ignition of the detonating cord, the granulated chemicals are explosively propelled through the clogged perforations in the oil well casing and penetrate into the wells surrounding coagulated geologic formation, to chemically react therewith to promote oil flow therethrough.